The present invention relates to a stator of an electric motor, the electric motor comprising such a stator and a method for producing such a motor. The invention relates for example to motors with magnets.
Such motors are for example used for moving flight surfaces in an aircraft with electric flight controls.
A motor generally comprises a rotor mounted so as to pivot in a stator formed by a bundle of laminations defining poles surrounded by electric circuits in coils in order to constitute electrical phases for driving the motor.
Some drive devices comprise a first motor and a second motor that are connected to the same movable element in order both to be able to drive this element independently of each other. The rotors of the two motors may for this purpose be connected to the same shaft.
In nominal operating mode, only the first motor is controlled so as to drive the element; the second motor is used only in the event of failure of the first motor.
An actuator having two or even three motors having a common output shaft has also been envisaged. Three stators are then mounted along the shaft, each opposite a portion of the shaft that is arranged to form a rotor. This solution is less heavy and less bulky while satisfying the same safety requirements as the previous solution.
This redundancy affords more safety in the functioning of the drive device to the detriment however of a relatively high mass of the drive device.
Furthermore, some breakdowns of the motor or of its control electronics may lead the motor to exert a braking force. The motors must therefore be sized so as to be able to compensate for this braking force generated by the faulty motor. In particular, when the faulty motor has a short-circuit between phases, the driving of the element by the other motor causes the rotation of the rotor of the faulty motor, inducing in the short-circuited phases a current that cannot be discharged and causes the appearance of a torque.
The motors must therefore be sized so as to be able to move the element alone, taking account not only of external actions exerted on the element but also the torque that would be generated by a faulty motor. The motors must therefore be able to produce a higher torque, which increases their cost, size and mass.
The maximum short-circuit torque CCC has the value CCC=3/2·K2/(2 p·(L−M)) and appears at the speed V=R/(p·(L−M)) with a slope with the origin equal to 3/2·K2/R where K is the phase/neutral torque coefficient, p is the number of pairs of poles, L is the inductance of the motor, M is the mutual phase/neutral inductance and R is the phase/neutral resistance.
To limit this torque, increasing the resistance of the coils in order to increase the rotation speed of the rotor at which the maximum torque appears is known. This solution can be envisaged only for motors working at low speed. This also increases the losses by Joule effect, degrading the performance of the motor and making cooling of the motor necessary.
Other solutions exist that require significant action on the magnetic circuit and assume modifications to the industrial processes for manufacturing the motors that are just as great. One of these solutions consists of reducing the flux of the magnets and compensating for this reduction in the flux by providing a more or less great protrusion of the laminations (reluctance motors).